Patent GB-1031384-A (GB)
Title: Grinding machine
IPC: B24B47/04
Filed: 1962-12-06
Abstract: 1,031,384. Grinding machines. HEALD MACHINE CO. Dec. 6, 1962 [Dec. 13, 1961], No. 46080/62. Heading B3D. A machine for use in grinding the internal surfaces of such workpieces as miniature ballbearing races comprises a work head 34, Fig. 5, wheel head 41 for supporting and rotating a spindle 42 carrying an abrasive wheel 43 at its outer end, and means for bringing about relative horizontal movement between the two heads transversely of the axis of the workpiece which, as shown at 91, Fig. 15, is supported on the work-head in a V-shaped recess defined by the surface of a rotatable disc 59 and the flat contact surface 89 of a shoe 88. The wheel head 41 is mounted on a table 31 arranged for reciprocation on a base 29 when the abrasive wheel is disposed inside the bore of the workpiece which is carried by the work head 34 on a table 33 arranged for feed and reverse movements transversely to the axis of the wheel on a carriage 32 movable on the base 29 in the same direction. The machine is described as under the control of pressure oil and pneumatic cylinders arranged in suitable circuits as shown in Fig. 50 for control through solenoid valves by an electric circuit including the various motors and limit switches so that the machine may carry out automatic grinding, dressing and compensation cycles. Control means on the machine panel provide for the setting and individual control of the parts, and lamps signal the various operations as they are carried out. The shoe 87 and rotatable disc 59 are carried on the body portion 55, Fig. 7, of the work-head 34 which also carries a further rotatable disc 61, Fig. 15, for urging the workpiece into its grinding position. Workpieces are fed one by one to this position from a shoot 94 by a feed finger 97 which is actuated through linkage from a piston 113 operating in a pneumatic cylinder 112, Figs. 7 and 50, so as to move up the inclined edge of the shoe 87 and push the lowermost workpiece in the shoot into grinding position, this workpiece simultaneously pushing the previously finished one to a discharge receptacle. The two discs 59, 61 are rotated through a belt drive from an electric motor and the disc 61 is carried by a lever 77 which is mounted at its outer end with a spring plunger 81, Fig. 10, coacting with a weaker spring plunger 126; the latter plunger is so controlled by air pressure from a valve 110, Fig. 7, operating in association with the piston 113 that, while a workpiece is being fed into grinding position, the disc 61 is acted upon only by the weaker plunger and so can readily be cammed upwardly by the workpiece, and, when the workpiece is in position, the strong plunger is effective to urge the disc into contact with the workpieee. Subsequent operations are set into operation by a contact 86 on the lever 77 closing a switch in the control circuit as the disc 61 is cammed upwardly. The work-table 33, Fig. 12, is movable on ball-bearing guides on the carriage 32 and its forward feed is effected by supplying liquid pressure to a hollow stud 148 (see also Fig. 50) projecting from a block 145 on the carriage into a bore 153 in a block 152 at the rear of the table. Feed of the table in this way is resisted by feed rate control mechanism disposed in a box 53, Figs. 5 and 22, on the carriage 32 at the forward edge of the table and comprising a cam 167 which is driven through gearing and clutches from a motor and actuates through a follower 168 a pin 171 engaging the front edge of the table; the motor is controlled so that it changes over from coarse to fine feed when the table actuates a switch 636, Fig. 50, in the control circuit. At the end of a cycle on a workpiece a spring-urged piston rack 172, Figs. 22 and 50, is forced by air pressure supplied to its cylinder 175 to reset the cam 167 without affecting the drive motor. With this method of feed the liquid supplied to the stud 148 from a source 518, Fig. 50, is at high pressure, but if the controlled force method of feeding is used the feed rate mechanism is immobilized and a valve 521 set to deliver the liquid at lower pressure. Withdrawal of the table to its initial position is effected by admitting pressure oil to a cylinder 144, Fig. 50, to withdraw a headed piston-rod 142, Fig. 12, having a slotted connection with the rear edge of the table. The work head is given a compensating movement after dressing the abrasive wheel by mechanism in the form of a screw 192, Fig. 25, which is carried in a housing 193 from the base 29 and engages a nut 191 on the carriage 32. The screw has a sleeve extension 205 which has screw-threaded engagement with a sleeve 206 carried from the housing and a splined connection with the outlet shaft 203 of a planetary gear system 202. This mechanism is operated for compensation by pressure oil introduced into a piston-and-cylinder device 239, Fig. 50, to rotate a yoke 228, Fig. 25, and so act through a clutch 226 to rotate the sun gear 223, planetary gear 222 and screw 192, the amount of compensation being set by adjustable stops co-operating with the yoke 228. The compensation mechanism may be reversed by movement of the yoke 228 without affecting the sun gear, or rapid reverse when it is desired to instal a new abrasive wheel may be carried out from a motor 194 which drives the outer ring gear 221 when an electric clutch 246 is activated to lock the sun gear. Three switches on the base 29 and arranged in the control circuit are set for sequential operation by adjustable contacts on the carriage 32 to respectively cause rearward movement of the carriage when the abrasive wheel is worn to an extent requiring its replacement, stop the carriage in its desired rearward position where the exchange of wheels is to be made, and set the position of the carriage when moved by the motor at which dressing and compensation are subsequently to take place. The wheel head 41 comprises a main portion 261, Fig. 31, slidable on rails on the base 29 to and from the work-head and an upper portion 259, which carries two electric motors operable at different frequencies and an air turbine for the selective drive of the abrasive wheel and is mounted for swivelling movement on the portion 261 about a vertical pin 262 so that the abrasive wheel may be located either coaxially with the workpiece or swung to one side when it is to be dressed to conical form. This swivelling motion is carried out by regulating the supply of pressure oil to a cylinder 271, Figs. 31 and 50, on the main portion 261 to control the piston 272 in relation to adjustable stops on the upper portion. Springs 265, Fig. 31, urge the upper and main portions together. The wheel head is reciprocated while in contact with the workpiece by an electric motor 46, Fig. 5, driving a vertical shaft 326, Fig. 38, which is journalled in a block 309 on the base 29 and has an adjustable cam 332 coacting with a follower roller 340 floatingly carried by pins 344 from a member 308 on the main portion 261 of the head. The roller is connected to the rod 338, Fig. 40, of the piston 337 of a pressure oil cylinder 335 secured to the member 308; the piston is spring-urged to the right and carries a tapered stem 354 movable in a narrow bore 349 at the end of the cylinder. By this arrangement, rightward movement of the piston, after initially forcing oil from the right hand end of the cylinder past the stem 354 and through a bore 356 in the piston, is strenuously resisted as the stem 354 passes along the bore 349, a diaphragm 353 at the end of the bore being forced into a counterbore 352 to exercise a spring effect; in the reverse direction of movement, oil passes rightwards through a further bore 357 in the piston. The wheel head is moved to and from its reciprocating position by feeding pressure oil into one end or the other of a cylinder 311, Figs. 38 and 50, so that its piston 312, which has the rod 313 connected to the main portion 261 of the wheel head, correspondingly moves the latter; throttling means embodied in the piston brake its movement to the right. A plug gauge 506, Fig. 50, mounted on the work-head is arranged for control by advancing and retracting pneumatic cylinders 505, 506 which are so operated by a solenoid valve 498 that at the time when the table 33 is changed over to fine feed the gauge attempts to enter the workpieee and when it succeeds in so doing, with the workpiece then ground to size, it closes a switch 631 to cause its retraction. The mechanism for dressing the abrasive wheel is arranged to be operated automatically after the finishing of any pre-set number of workpieces and comprises a diamond 366, Fig. 47, at the end of an arm 365 mounted on a shaft 367 in a body 362 carried from a block 359 on the carriage 32 by flexible reeds 363, 364. The shaft 367 is fitted with a gear 371 engaging a spring-urged piston rack 372 in a pressure oil cylinder 376 (see also Fig. 50) which can be energized to swing the diamond between its upper inoperative and horizontal operative position. In the latter position, the diamond is traversed by the abrasive wheel, the upper portion 259, Fig. 31, of the wheel head being then swivelled to one side about the vertical pivot 262 by means of the pressure oil cylinder 271 so that the wheel is dressed to such conical shape as will compensate for the deflection of the abrasive wheel spindle which takes place during grinding. Since the size of the bore being ground is affected as the machine becomes heated in use, the diamond is given an automatic compensating movement by arranging for the body 362 to be moved correspondingly on the flexible reeds 363, 364 by the action of the end 391 of a lever 388 (which is pivoted on the block 359) when the opposite end of the lever is swung by its coaction with a shaft 398, Fig. 48, which has screw-threaded engagement in the body 362 and is rotated through worm gearing 402, 403, from a reversible motor 406. Relays for forward and reve